Chip multi-processors (CMPs) contain several processors on the same die. In a shared-cache CMP, some level of the cache is shared and is accessed by some or all of the processors on the chip. Often, this sharing is beneficial, because the processors are executing a multi-threaded software application in which the threads share data and instructions. By sharing the cache, a word of data that is accessed by more than one processor occupies a single location in the cache. Moreover, any processor can use all the cache if needed and allowed by the other processors. The downside of sharing the cache is that if the processors collectively require more capacity than available, they can experience more overall cache misses than if they had smaller private caches.
In a set-associative cache memory, a cache miss of requested data within the cache memory requires eviction of a block from the cache, referred to herein as the “victim block” to make room for the requested block. Accessing of the set-associative cache is performed according to an index of the cache request, which is used to select a set within the cache memory. Once the set is selected, a tag value of the cache request is used to identify a way within the selected set containing the requested cache block. When comparison of the tag value of the cache request fails to identify a corresponding way within the selected set, a cache miss is detected. In a shared cache, selection of the victim block to evict, in response to a cache miss, can become problematic depending on the number of processors which share the cache.